Optical element and imaging lens

ABSTRACT

An object is to provide an optical element and an imaging lens that reproduce clear images by restraining ghosting, flare, and/or similar occurrences caused by unwanted light reflected by the outer circumference surface of an edge of the optical element. An optical element  100  includes an optical effective portion  101  and an edge  102 . The edge  102  is located around the optical effective portion  101  and has an outer circumference surface  103 . The outer circumference surface  103  includes roughened portions  200 . An imaging lens uses the optical element  100.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 toJapanese Patent Application No. 2018-099067, filed May 23, 2018. Thecontents of this application are incorporated herein by reference intheir entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an optical element used in an imagingdevice and relates to an imaging lens using the optical element.

Discussion of the Background

In recent years, a variety of products such as information terminalshave been equipped with camera functions.

For cameras built in these information terminals, there is a need forimaging lenses capable of taking clear images, with eliminated orminimized ghosting and flare. In order to eliminate or minimize ghostingand flare, it is important to restrain unwanted light, which does notcontribute to image formation.

Patent documents 1 and 2 disclose techniques to restrain unwanted light.

Patent document 1 discloses an optical element incorporated in aphotographing optical system. The optical element includes an effectivediameter area, an outside effective diameter area, and an outercircumference surface. The effective diameter area is centered around aphotographing optical axis, and permits an effective light flux thatcontributes to image formation to pass through the effective diameterarea. The outside effective diameter area surrounds the effectivediameter area. The outer circumference surface surrounds the outsideeffective diameter area. At least a part of the outer circumferencesurface in its thickness direction or circumferential direction is anon-parallel surface having an angle relative to the photographingoptical axis. When a ray of light enters the optical element through theobject-side surface of the optical element and is reflected on theimage-side surface of the optical element to become incident on andreflected by the outer circumference surface, the non-parallel surfaceprevents the reflected ray of light from becoming incident on the imageside of the optical element.

Patent document 2 discloses a lens unit that includes a photographingoptical system and a photographing optical system holder. Thephotographing optical system includes a plurality of optical elementsand forms an optical image of an object. The photographing opticalsystem holder holds the photographing optical system. At least oneoptical element among the plurality of optical elements includes aneffective region portion, a non-effective region portion, an engagementdepression or an engagement protrusion, and a scattering portion. Theeffective region portion permits a light flux from an object to passthrough the effective region portion. The non-effective region portionsurrounds the effective region portion in an orthogonal directionorthogonal to an optical axis of the photographing optical system. Theengagement depression or the engagement protrusion is located betweenthe effective region portion and the non-effective region portion in theorthogonal direction, and is engaged with an adjacent optical element sothat the optical axis of the at least one optical element and theoptical axis of the adjacent optical element coincide. The scatteringportion is located on the outer circumference surface of thenon-effective region portion and scatters light. The term scatteringportion is recognized as: “The scattering portion is an embossed layerformed by roughening the outer circumference surface of thenon-effective region portion. The embossed layer has a surface roughnessof equal to or less than approximately 10 μm, in ten-point averageroughness, preferably approximately 4 to 6 μm. Surfaces having thespecified surface roughnesses can be formed using a roughness die suchas #1003, available from AYAMADAI CO., LTD.” (see paragraph [0033] ofpatent document 2).

RELATED ART DOCUMENTS Patent Documents

[Patent document 1] JP 2010-164755A

[Patent document 2] JP 2015-90484A

Problems to be Solved by the Invention

In the optical element recited in patent document 1, at least a part ofthe outer circumference surface in its thickness direction orcircumferential direction is a non-parallel surface having an anglerelative to the photographing optical axis. With this configuration, theobject of patent document 1 is to control reflection light away from theimaging element side. This optical element, however, provides no orlittle effect of attenuating the power of reflection light, and thus isinsufficient in restraining unwanted light occurring in the imaginglens.

In an attempt to attenuate the power of reflection light, the imaginglens recited in patent document 2 has an embossed layer to scatter lighton the outer surface of the imaging lens, in addition to having theconfiguration of the optical element recited in patent document 1.However, the mere formation of an embossed layer is insufficient forrestraining unwanted light, which does not contribute to imageformation.

The present invention has been made in light of the above-describedcircumstances, and has an object to sufficiently restrain unwantedlight, which does not contribute to image formation, by providing theouter circumference surface of an optical element with a shape thatsufficiently restrains reflection light. The present invention also hasan object to provide an imaging lens using the optical element.

SUMMARY OF THE INVENTION

In order to accomplish the above-described object, an optical elementaccording to an embodiment of the present invention includes an opticaleffective portion and an edge. The edge is located around the opticaleffective portion and has an outer circumference surface. The outercircumference surface includes a roughened portion.

In order to accomplish the above-described object, an imaging lensaccording to an embodiment of the present invention includes opticalelement having the following configuration. The optical element includesan optical effective portion and an edge. The edge is located around theoptical effective portion and has an outer circumference surface. Theouter circumference surface includes a plurality of roughened portions.

Effects of the Invention

The embodiments of the present invention ensure that when light in theoptical element becomes incident on and reflected by the outercircumference surface, the plurality of roughened portions attenuate thepower of the light sufficiently for restraining ghosting and flare.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a schematic illustrating an optical element according to anembodiment of the present invention;

FIG. 2 is a cross-sectional view of the optical element according to theembodiment of the present invention;

FIG. 3 is a schematic illustrating a behavior of unwanted light onroughened portions of an outer circumference surface of the opticalelement;

FIG. 4 is an enlarged view of part (103) illustrated in FIG. 1,illustrating one embodiment of the roughened portion;

FIG. 5 is a cross-sectional view of one embodiment of an imaging lensstructure to which the optical element according to the embodiment ofthe present invention is applied;

FIG. 6A illustrates unwanted light occurring in a conventional imaginglens, and FIG. 6B illustrates unwanted light occurring in the embodimentillustrated in FIG. 5, in which the optical element according to theembodiment of the present invention is applied to an imaging lens; and

FIG. 7A illustrates unwanted light occurring in a conventional imaginglens, and FIG. 7B illustrates unwanted light occurring in the embodimentillustrated in FIG. 5, in which the optical element according to theembodiment of the present invention is applied to an imaging lens.

In the optical element according to the embodiment of the presentinvention, the outer circumference surface of the edge formed around theoptical effective portion of the optical element includes a roughenedportion. The roughened portion attenuates unwanted light reflected bythe outer circumference surface of the optical element.

The embodiments of the present invention will be described in detailbelow by referring to FIGS. 1 to 7.

FIG. 1 illustrates the optical element according to one embodiment ofthe present invention.

As illustrated in FIG. 1, an optical element 100 includes an opticaleffective portion 101 and an edge 102. The optical effective portion 101is where effective rays of light enter. The edge 102 is formed aroundthe optical effective portion 101 and integral to the optical effectiveportion 101. The edge 102 has an outer circumference surface 103. Theouter circumference surface 103 includes a plurality of roughenedportions 200.

FIG. 2 is a cross-sectional view of the optical element 100 taken alongA-A′ illustrated in FIG. 1.

As illustrated in FIG. 2, the roughened portions 200 of the outercircumference surface 103 extend in parallel to the direction in whichthe optical axis, X, of the optical element 100 extends. It is to benoted that the roughened portions 200 may extend with an angle relativeto the optical axis X.

FIG. 3 illustrates a behavior of a ray of light SL incident on theroughened portions 200 of the outer circumference surface 103.

As illustrated in FIG. 3, when the ray of light SL becomes incident onthe roughened portions 200 of the outer circumference surface 103, theray of light SL turns into scattered light with attenuated light power.

Details of the shape of each roughened portion 200 may be set usingghosting simulation software to form a shape that highly accuratelycontrols the directions in which the ray of light SL is reflected. Thatis, an analysis for restraining ghosting and flare can be performed atthe design stage.

This eliminates or minimizes the need for the conventionaltrial-and-error type of procedure that involves: evaluating theoccurrence of ghosting and flare after an imaging lens has beenassembled; analyzing the ghosting and flare for the cause of theghosting and flare; and feeding the analysis back to the design stage.

Also, forming a roughened shape to scatter light is more effective forrestraining ghosting and flare than the mere formation of an embossedlayer.

It is preferable, therefore, to form an embossed layer on the surfacesof the roughened portions 200 of the outer circumference surface 103.

FIG. 4 illustrates one embodiment of a shape of the roughened portion200. In this embodiment, the roughened portion 200 has a height H of0.065 mm; an edge portion E1 of an arcuate protrusion of the roughenedportion 200 has a radius (R) of R 0.05 mm; and an edge portion E2 of anarcuate depression of the roughened portion 200 has a radius (R) of R0.15 mm. The roughened portion 200 thus dimensioned has a unit shapemade up of a protrusion and a depression, and a repetition of 72 unitshapes is formed over the entire circumference of the outercircumference surface of the edge (at a pitch P of 5° (degrees) relativeto the optical axis X).

It is to be noted that the shape of the roughened portion 200 will notbe limited to the above-described dimension values. The roughenedportion 200 may have any other shape insofar as, preferably, the heightH is equal to or more than 0.01 mm, the edge portion E1 of theprotrusion of roughened portion 200 has a radius (R) of equal to or morethan 0.03 mm, and the edge portion E2 of the depression of roughenedportion 200 has a radius (R) of equal to or more than 0.03 mm. Also, theroughened portions 200 may be formed partially on the outercircumference surface of the edge, that is, at necessary portions of theouter circumference surface of the edge such that the repetition of theprotrusion-depression unit shapes is equal to or more than ten (thepitch P is equal to or less than 36° (degrees) relative to the opticalaxis X).

FIG. 5 illustrates one embodiment in which the optical element 100 isapplied to an imaging lens 300, which is made up of six opticalelements. In this embodiment, the optical element 100 is applied to oneof the six optical elements.

As illustrated in FIG. 5, the imaging lens 300 includes a barrel 302, afirst lens L1, a second lens L2, a third lens L3, a fourth lens L4, afifth lens L5, a sixth lens L6, and a rear light-shielding ring 304. Thefirst lens L1, the second lens L2, the third lens L3, the fourth lensL4, the fifth lens L5, the sixth lens L6, and the rear light-shieldingring 304 are contained in the barrel 302 in this order from the objectside (from the upper side of FIG. 5) toward the side of imaging elementIMG (toward the lower side of FIG. 5).

A light shielding plate 303 is located between the first lens L1 and thesecond lens L2; a light shielding plate 303 is located between thesecond lens L2 and the third lens L3; a light shielding plate 303 islocated between the third lens L3 and the fourth lens L4; a lightshielding plate 303 is located between the fourth lens L4 and the fifthlens L5; and a light shielding plate 303 is located between the fifthlens L5 and the sixth lens L6.

The rear light-shielding ring 304 is a member that fixes the first tosixth lenses L1 to L6 in the optical axis X direction and that is fixedby welding to the inner surface of the barrel 302 using a solvent suchas methyl acetate. It is to be noted that the method of fixing the rearlight-shielding ring 304 to the barrel 302 will not be limited towelding, other examples including bonding, press fitting, and acombination of the foregoing.

Also, the material of the lens constituting each of the optical elementsis an optical-purpose resin such as cycloolefin polymer andpolycarbonate. Also, the optical elements are formed by injectionmolding.

The imaging lens 300 is applicable to, for example, small-size imaginglenses used in mobile phones and smartphones. A filter IR to cutinfrared light is disposed at the imaging element IMG side of theimaging lens 300. Next to the filter IR, the imaging element IMG isdisposed. Examples of the imaging element IMG include, but are notlimited to, a CCD sensor and a C-MOS sensor. Thus, the imaging lens 300,the filter IR, and the imaging element IMG are packaged into a cameramodule.

Each of the lenses has an optical effective portion (lens portion) andan edge formed around the optical effective portion. The edge of eachlens has a protrusion engaged with an adjacent lens. The protrusion hasan approximately trapezoid shape that includes a conical inclinedsurface and a plane portion connected to the inclined surface.

Next, how the imaging lens 300 is structured will be described.

A plane portion L1 a of the edge of the first lens L1 is brought intocontact with a receiving surface 302 a. The receiving surface 302 a isformed on the inner surface of the barrel 302 and is perpendicular tothe optical axis X. In this manner, the position of the first lens L1 inthe optical axis X direction is determined.

Also, an outer surface L1 c of the first lens L1 is brought intoengagement with an inner diameter portion 302 b of the barrel 302. Inthis manner, the first lens L1 and the barrel 302 are subjected to axisalignment such that the first lens L1 and the barrel 302 are alignedwith each other on the optical axis X.

Next, an inclined surface L1 b of the first lens L1 is brought intoengagement with an inclined surface L2 a of the second lens L2. In thismanner, the first lens L1 and the second lens L2 are subjected to axisalignment such that the first lens L1 and the second lens L2 are alignedwith each other on the optical axis X.

Next, an inclined surface L2 b of the second lens L2 is brought intoengagement with an inclined surface L3 a of the third lens L3. In thismanner, the second lens L2 and the third lens L3 are subjected to axisalignment such that the second lens L2 and the third lens L3 are alignedwith each other on the optical axis X.

Next, an inclined surface L3 b of the third lens L3 is brought intoengagement with an inclined surface L4 a of the fourth lens L4. In thismanner, the third lens L3 and the fourth lens L4 are subjected to axisalignment such that the third lens L3 and the fourth lens L4 are alignedwith each other on the optical axis X.

Next, an inclined surface 5 b of the fifth lens L5 is brought intoengagement with an inclined surface L 6 a of the sixth lens L6. In thismanner, the fifth lens L5 and the sixth lens L6 are subjected to axisalignment such that the fifth lens L5 and the sixth lens L6 are alignedwith each other on the optical axis X.

Next, an outer surface L6 c of the sixth lens L6 is brought intoengagement with an inner diameter portion 302 c of the barrel 302. Inthis manner, the sixth lens L6 and the barrel 302 are subjected to axisalignment such that the sixth lens L6 and the barrel 302 are alignedwith each other on the optical axis X.

In the above-described structure of the imaging lens 300, a lensassembly 301 results with such a structure that the centers of the firstto sixth lenses L1 to L6 are aligned with each other on the optical axisX and that the center of the barrel 302 is aligned with the centers ofthe first to sixth lenses L1 to L6 on the optical axis X.

Also in the above-described structure of the imaging lens 300, the firstto fourth lenses L1 to L4 and the fifth and sixth lenses L5 and L6 eachhave a protrusion at the edge of each lens. The protrusion includes aninclined surface and a plane portion connected to the inclined surface.The plane portion is in contact with the plane portion of the edge of anadjacent lens. The contact between the plane portions determines the gapbetween one lens and an adjacent lens. It is to be noted that the gapbetween the fourth lens L4 and the fifth lens L5 is determined by thethickness of the light shielding plate 303.

Thus, the centers of the lenses of the lens assembly 301 are broughtinto alignment with each other on the optical axis X by the meresuperposition of the lenses on top of each other. At the same time, thesuperposition of the lenses on top of each other determines the gapsbetween the lenses.

It is to be noted that the light shielding plate 303 located between onelens and an adjacent lens is a flat annular light shielding member withan opening at the center of the annular light shielding member.

The diameter of the opening of the light shielding plate 303 is set at aminimum possible diameter that does not obstruct passage of a light fluxB0 and a light flux B1. The light flux B0 is a flux of effective rays oflight that become incident on the imaging lens 300 and collect on theoptical axis X. The light flux B1 is a flux of effective rays of lightincident that become incident on the imaging lens 300 from a maximumfield angle and that collect to a maximum image height. Rays of lightincident from positions outer than the light flux B1 are blocked by thelight shielding plate 303. Thus, the light shielding plate 303 blocksunwanted light while permitting effective rays of light to pass throughthe light shielding plate 303.

FIG. 5 illustrates an embodiment in which the optical element 100 isapplied to the fifth lens L5 among the first to sixth lenses L1 to L6 ofthe imaging lens 300.

Next, by referring to the embodiment illustrated in FIG. 5, descriptionwill be made with regard to how the optical element 100 attenuates thepower of reflection light that can cause ghosting and flare.

FIG. 6A is a schematic illustrating a state in which unwanted light isoccurring in a conventional imaging lens 300′, and FIG. 6B is aschematic illustrating a state in which the imaging lens 300 illustratedin FIG. 5 restrains unwanted light.

As illustrated in FIG. 6A, the ray of light SL passes through theimaging lens 300′; is reflected by the upper surface of the filter IR;enters the edge of the sixth lens L6; passes through the portion ofengagement between the sixth lens L6 and the fifth lens L5; is reflectedby the outer surface of the fifth lens L5; is totally reflected by theeffective diameter portion of the fifth lens L5; passes through thefilter IR; and reaches the imaging element IMG.

The ray of light SL reaching the imaging element IMG appears in thephotographed image in the form of ghosting and/or flare, to thedetriment of image quality.

FIG. 6B illustrates an example in which the optical element 100(according to the above-described embodiment of the present invention)is applied to the fifth lens L5 of the imaging lens 300′ illustrated inFIG. 6A. Specifically, the roughened portions 200 are formed on theouter circumference surface 103 of the fifth lens L5 of the imaging lens300′.

As illustrated in FIG. 6B, the ray of light SL passes through theimaging lens 300; is reflected by the upper surface of the filter IR;enters the edge of the sixth lens L6; passes through the portion ofengagement between the sixth lens L6 and the fifth lens L5; becomesincident on the outer surface of 103 of the fifth lens L5; and isscattered by the roughened portions 200 of the outer circumferencesurface 103. This attenuates the power of the light incident on andreflected by the outer surface of the fifth lens L5.

Thus, the ray of light SL scattered by the roughened portions 200 of theouter surface of the fifth lens L5 has been attenuated in light power.This prevents the ray of light SL from being totally reflected by theeffective diameter portion of the fifth lens L5 and reaching the imagingelement IMG through the filter IR. This effectively restrains occurrenceof ghosting and flare.

FIG. 7A is a schematic illustrating a state in which unwanted light isoccurring in the conventional imaging lens 300′, and FIG. 7B is aschematic illustrating a state in which the imaging lens 300 illustratedin FIG. 5 restrains unwanted light.

As illustrated in FIG. 7A, unwanted light SL is reflected by a surfaceof the edge of the fifth lens L5 of the imaging lens 300′; is reflectedby the outer circumference surface 103 of the fifth lens L5; is totallyreflected by the effective diameter portion of the fifth lens L5; passesthrough the filter IR; and reaches the imaging element IMG. The ray oflight SL reaching the imaging element IMG appears in the photographedimage in the form of ghosting and/or flare, to the detriment of imagequality.

FIG. 7B illustrates an example in which the optical element 100(according to the above-described embodiment of the present invention)is applied to the fifth lens L5 of the imaging lens 300′ illustrated inFIG. 7A. Specifically, the roughened portions 200 are formed on theouter circumference surface 103 of the fifth lens L5 of the imaging lens300′.

As illustrated in FIG. 7B, the unwanted light SL is reflected by asurface of the edge of the fifth lens L5 of the imaging lens 300;becomes incident on the outer circumference surface 103 of the fifthlens L5; and is scattered by the roughened portions 200 of the outercircumference surface 103. This attenuates the power of the lightincident on and reflected by the outer surface of the fifth lens L5.

Thus, the unwanted light SL scattered by the roughened portions 200 ofthe outer surface of the fifth lens L5 has been attenuated in lightpower. This prevents the unwanted light SL from being totally reflectedby the effective diameter portion of the fifth lens L5 and reaching theimaging element IMG through the filter IR. This effectively restrainsoccurrence of ghosting and flare.

As has been described hereinbefore, in the optical element according tothe embodiment of the present invention and in the imaging lens usingthe optical element, roughened portions to restrain unwanted light areformed on the outer surface of the edge around the optical effectiveportion. This effectively restrains occurrence of ghosting and flare.

In the above description, the optical element according to theembodiment of the present invention is applied to the fifth lens of animaging lens made up of six lenses. This configuration, however, is notintended in a limiting sense; the optical element may be applied to anyother portion of an imaging lens where it is necessary to restrain lightreflection on the outer circumference of the optical element. It is alsopossible to apply the optical element according to the embodiment of thepresent invention to a plurality of lenses of an imaging lens, or to animaging lens made up of a single optical element.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention effectively restrain lightreflection in optical elements, and, when applied to imaging devicesrequiring high image quality, contribute to improvement of opticalperformance and quality of the imaging devices.

DESCRIPTION OF REFERENCE NUMERAL

-   100 Optical element-   101 Optical effective portion (lens portion)-   102 Edge-   103 Outer circumference surface-   200 Roughened portion-   300, 300′ Imaging lens-   301 Lens assembly-   302 Barrel-   303 Light shielding plate-   304 Rear light-shielding ring-   L1 First lens-   L2 Second lens-   L3 Third lens-   L4 Fourth lens-   L5 Fifth lens-   L6 Sixth lens-   L1 b, L2 a, L2 b, L3 a, L3 b, L4 a, L5 b, L6 a Lens engagement    portion-   L1 a, L1 c, L6 c, 302 a, 302 b, 303 c Barrel engagement portion-   B0 Effective light flux on optical axis-   B1 Effective light flux at maximum image height-   SL Ray of light, unwanted light-   X Optical axis-   IR Filter-   IMG Imaging device

1. An optical element comprising: an optical effective portion; and anedge located around the optical effective portion and having an outercircumference surface, the outer circumference surface comprising aroughened portion.
 2. The optical element according to claim 1, whereinthe roughened portion has a unit shape comprising a protrusion and adepression, and the unit shape comprises a repetition of equal to ormore than ten unit shapes.
 3. The optical element according to claim 1,wherein the roughened portion protrudes in a radiation directiondirected from an optical axis of the optical element toward the outercircumference surface, and has a protrusion height of equal to or morethan 0.01 mm.
 4. The optical element according to claim 1, wherein theroughened portion comprises a depression and a protrusion, thedepression or the protrusion extending in an extension direction inwhich the optical axis extends, the extension direction being parallelto the optical axis.
 5. The optical element according to claim 1,wherein the roughened portion comprises a depression and a protrusion,the depression or the protrusion extending in an extension direction inwhich the optical axis extends, the extension direction having an anglerelative to the optical axis.
 6. The optical element according to claim1, wherein the roughened portion has a continuous shape extending overthe outer circumference surface.
 7. The optical element according toclaim 1, wherein the roughened portion comprises an arcuate depressionand an arcuate protrusion each having a radius of equal to or more than0.03 mm.
 8. An imaging lens comprising the optical element according toclaim
 1. 9. An imaging lens comprising the optical element according toclaim
 2. 10. An imaging lens comprising the optical element according toclaim
 3. 11. An imaging lens comprising the optical element according toclaim
 4. 12. An imaging lens comprising the optical element according toclaim
 5. 13. An imaging lens comprising the optical element according toclaim 6.